The channel corner and the portion that needs to change the flow velocity are subject to convergence and divergence of the channel in a variety of thermal industrial applications; therefore, the present research is to improve the design of converging and diverging cooling passage in the thermal systems. In order to meet the requirement, The experimental measurements of heat transfer and friction factors in the converging and diverging ribbed channels are done. The Reynolds numbers range from 20,000 to 90,000.
The dimensions of test section are 100 mm x 75 mm and 100 mm x 50 mm at cross section of the exit and 100 mm x 100 mm at the inlet in the converging channel; 100 mm x 100 mm at the exit, and 100 x 75 mm and 100 x 50 mm at the inlet in the diverging channel. The uniform cross-sectional channel of 100mm x 100 mm is considered as a reference.
Copper plates fitted with silicone heaters and thermocouples are installed at the interval of 100 mm on the left and right sided side wall only. The rib height() transversely installed only the left side wall is 10 mm and spacing() to height ratio () is 10. The left and right sided walls at test section with length of 1 m are divided into 10 regions, and each region has one copper plate (100 mm x 100 mm x 2 mm(t)).
Air is used as a working fluid and the air is induced to the test section from the blower. Because of the streamwise flow acceleration or deceleration, the heat transfer and friction factors are quite different from those of the straight channel.
The major findings are as follows :
1. The Nusselt numbers in the converging channel are less than in the uniform cross-sectional channel.
2. The friction factors increase with increasing the convergence ration in the converging channel.
3. The Nusselt numbers and effective friction factors increase with increasing the divergence ratio in the diverging channel.
4. The design of diverging channel is advantageous over the converging channel, and the design of is best.